Re: [PATCH 13/27] gpu: nova-core: generalize allocate_command() for variable headers

[Zhi Wang <zhiw@nvidia.com>]

On Tue, 18 Aug 2026 20:52:06 -0700
John Hubbard <jhubbard@nvidia.com> wrote:

Looking good to me.

Reviewed-by: Zhi Wang <zhiw@nvidia.com>

> The GMC command path uses a different message element header from the
> VGPU-style RPC path, but the two share the queue, the space
> accounting, and the wrapping rules. Make allocate_command() and
> GspCommand generic over the header type, defaulting to GspMsgElement
> so the existing RPC callers are unchanged.
> 
> No functional changes.
> 
> Assisted-by: Cursor:claude-opus-5
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
>  drivers/gpu/nova-core/gsp/cmdq.rs | 22 +++++++++++++++-------
>  1 file changed, 15 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/nova-core/gsp/cmdq.rs
> b/drivers/gpu/nova-core/gsp/cmdq.rs index 1d86d2927a94..0dab3d279426
> 100644 --- a/drivers/gpu/nova-core/gsp/cmdq.rs
> +++ b/drivers/gpu/nova-core/gsp/cmdq.rs
> @@ -365,6 +365,8 @@ fn driver_write_area_size(&self) -> usize {
>      /// Allocates a region on the command queue that is large enough
> to send a command of `size` /// bytes, waiting for space to become
> available based on the provided timeout. ///
> +    /// The type parameter `H` selects the message element header,
> [`GspMsgElement`] for RM RPC.
> +    ///
>      /// This returns a [`GspCommand`] ready to be written to by the
> caller. ///
>      /// # Errors
> @@ -372,13 +374,17 @@ fn driver_write_area_size(&self) -> usize {
>      /// - `EMSGSIZE` if the command is larger than
> [`GSP_MSG_QUEUE_ELEMENT_SIZE_MAX`]. /// - `ETIMEDOUT` if space does
> not become available within the timeout. /// - `EIO` if the command
> header is not properly aligned.
> -    fn allocate_command(&mut self, size: usize, timeout: Delta) ->
> Result<GspCommand<'_>> {
> -        if size_of::<GspMsgElement>() + size >
> GSP_MSG_QUEUE_ELEMENT_SIZE_MAX {
> +    fn allocate_command<H: FromBytes + AsBytes>(
> +        &mut self,
> +        size: usize,
> +        timeout: Delta,
> +    ) -> Result<GspCommand<'_, H>> {
> +        if size_of::<H>() + size > GSP_MSG_QUEUE_ELEMENT_SIZE_MAX {
>              return Err(EMSGSIZE);
>          }
>          read_poll_timeout(
>              || Ok(self.driver_write_area_size()),
> -            |available_bytes| *available_bytes >=
> size_of::<GspMsgElement>() + size,
> +            |available_bytes| *available_bytes >= size_of::<H>() +
> size, Delta::from_micros(1),
>              timeout,
>          )?;
> @@ -390,8 +396,8 @@ fn allocate_command(&mut self, size: usize,
> timeout: Delta) -> Result<GspCommand (slice_1.as_flattened_mut(),
> slice_2.as_flattened_mut()) };
>  
> -        // Extract area for the `GspMsgElement`.
> -        let (header, slice_1) =
> GspMsgElement::from_bytes_mut_prefix(slice_1).ok_or(EIO)?;
> +        // Extract area for the message element header.
> +        let (header, slice_1) =
> H::from_bytes_mut_prefix(slice_1).ok_or(EIO)?; 
>          // Create the contents area.
>          let (slice_1, slice_2) = if slice_1.len() > size {
> @@ -609,10 +615,12 @@ fn driver_read_area_v2(
>  
>  /// A command ready to be sent on the command queue.
>  ///
> +/// The type parameter `H` is the message element header type,
> [`GspMsgElement`] for RM RPC. +///
>  /// This is the type returned by [`DmaGspMem::allocate_command`].
> -struct GspCommand<'a> {
> +struct GspCommand<'a, H = GspMsgElement> {
>      // Writable reference to the header of the command.
> -    header: &'a mut GspMsgElement,
> +    header: &'a mut H,
>      // Writable slices to the contents of the command. The second
> slice is zero unless the command // loops over the command queue.
>      contents: (&'a mut [u8], &'a mut [u8]),